Tag Archives: PDF

PDF in three dimensions

There are two ways to put 3D models into a PDF file. Neither of them is an extension of the two-dimensional PDF model. Rather, they’re technologies which were developed independently, which can be wrapped into a PDF, and which software such as Adobe Acrobat can work with.

PDF has become a container format as much as a representational format. It can hold anything, and some of the things it holds have more or less official status, but there are no common architectural principles. The two formats used with PDF are U3D and PRC. Both are actually independent file formats which a PDF can embed.
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PDF/L?

Here’s a question for the gallery: Have any of you heard of PDF/L, and do you know what it is?
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File corruption and political corruption

When people who don’t understand file formats manipulate files in order to cover their tracks, they generally fail miserably. Slate magazine gives an entertaining case in point from the Trump scandals. The article says:

There are two types of people in this world: those who know how to convert PDFs into Word documents and those who are indicted for money laundering. Former Trump campaign chairman Paul Manafort is the second kind of person.

The PDF Association chimes in with additional technical details.
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JHOVE webinar

An Open Preservation Foundation webinar, “Putting JHOVE to the acid test: A PDF test-set for well-formedness validation in JHOVE,” will be held on November 21, 10 AM GMT (that’s 11 AM in Central Europe and a ludicrous 5 AM or earlier in the US).
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The PDF/A controversy

Is PDF/A a good archival format? Many institutions use it, but it has problems which are inherent in PDF. With PDF/A-3, it has lost some of its focus. A format which can be a container for any kind of content isn’t great for digital preservation.

An article by Marco Klindt of the Zuse Institute Berlin takes a strong position against its suitability, with the title “PDF/A considered harmful for digital preservation.” Carl Wilson at the Open Preservation Foundation has added his own thoughts with “PDF/A and Long Term Preservation.”

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PDF 2.0

The ISO specification for PDF 2.0 is now out. It’s known as ISO 32000-2. As usual for ISO, it costs an insane 198 Swiss francs, which is roughly the same amount in dollars. In the past, Adobe has made PDF specifications available for free on its own site, but I can’t find it on adobe.com. Its PDF reference page still covers only PDF 1.7.

ISO has to pay its bills somehow, but it’s not good if the standard is priced so high that only specialists can afford it. I don’t intend to spend $200 to be able to update JHOVE without pay. With some digging, I’ve found it in an incomplete, eyes-only format. All I can view is the table of contents. There are links to all sections, but they don’t work. I’m not sure whether it’s broken on my browser or by intention. In any case, it’s a big step backward as an open standard. I hope Adobe will eventually put the spec on its website.
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Figuring out the PDF version is harder than you think

In a GitHub comment, Johan van der Knijff noted how messy it is to determine the version of a PDF file. He looked at a file with the header characters “%PDF-1.8”. DROID says this isn’t a PDF file at all.

By a strict reading of the PDF specification, it isn’t. The version number has to be in the range 1.0 through 1.7. Being this strict seems like a bad idea, since it would mean format recognition software will fail to recognize any future versions of the format. (JHOVE doesn’t care what character comes after the period.)
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The steep road to supporting the PDF format

A lot of applications claim they can display PDF files, but not all of them fully support the format. They won’t necessarily display all valid files correctly. The PDF Association has an article discussing this problem, with the main focus on the Microsoft Edge browser.

Edge offers only partial support for the JBIG2Decode and JPXDecode filters, which means some objects might not display. It doesn’t support certain types of shadings, so other objects could render incorrectly.

The strength of PDF is supposed to be that it will render the same way everywhere. You can blame Microsoft for not putting enough work into it, or Adobe for making the format too complex. I have enough experience with it to know it’s a seriously difficult format just to analyze, to say nothing of rendering. Is a format which presents such difficulties really the ideal for a universal document rendering format that people will count on far into the future?

Update: It gets worse. Take a look at this discussion of what’s in PDF.

The state of PDF 2.0

The next big jump in PDF may finally happen this year. The PDF association tells us that the spec for PDF 2.0 is “feature-complete” and will be available to the ISO PDF committee and members of the PDF Association in July. When this will turn into a public release still isn’t clear. A year ago the target was “mid-2016”; that seems unlikely now.

The specification will be ISO 32000-2. The current version of PDF, 1.7, is ISO 32000-1. More precisely, Adobe has published several extension levels to PDF 1.7. They’re a way of getting around having a version 1.8, which would be an admission that the ISO standard is outdated. Version 2.0 will get Adobe and ISO back in sync. Hopefully Adobe will publish the PDF spec for free, as it has in the past, so that it won’t be available just to people who pay for the ISO version. Currently an electronic copy of ISO 32000-1 costs 198 Swiss francs, or a bit more than $200.
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PDF/A and forms

The PDF Association reminds us that we can use PDF forms for electronic submissions. It’s a useful feature, and I’ve filled out PDF forms now and then. However, one point seems wrong to me:

PDF/A, the archival subset of PDF technology, provides a means of ensuring the quality and usability of conforming PDF pages (including PDF forms) without any external dependencies. PDF/A offers implementers the confidence of knowing that conforming documents and forms will be readable 10, 20 or 200 years from now.

The problem is that PDF/A doesn’t allow form actions. ISO 19005-1 says, “Interactive form fields shall not perform actions of any type.” You can have a form and you can print it, but without being able to perform the submit-form action, it isn’t useful for digital submissions.

You could have an archival version of the form and a way to convert it to an interactive version, but this seems clumsy. Please let me know if I’ve missed something.

Update: There’s some kind of irony in the fact that the same day that I posted this, I received a print-only PDF form which I’ll now have to take to Staples to fax to the originator.